There are known TE lasers, such as one described in U.S. Pat. No. 4,240,044. In this system, a corona-discharge pre-ionizer is disposed near a side surface of one of the main electrodes, wherein a distance from the opposite electrode is greater than a distance between the work surfaces of the main discharge electrodes. The pre-ionizer, however, illuminates only a part of the discharge gap and only one opposite discharge electrode surface, which does not permit obtaining a stable discharge.
An electrode structure of another TE laser is taught in U.S. Pat. No. 6,546,036, which structure comprises corona-discharge pre-ionizers mounted inside of the main discharge electrodes. The pre-ionizers illuminate the whole discharge gap and don't block the gas flow in the discharge gap zone. Since the working surfaces of the main electrodes consist of several parts disposed distantly from each other, the discharge between the main electrodes becomes not uniform and not stable that reduces the quality of laser radiation.
An electrode structure of another TE laser is taught in a Russian Federation patent application RU2007100984. In this structure the inner corona-discharge pre-ionizer electrodes are connected by a conductor that permits obtaining a pre-ionization of the laser gas mixture without high voltage inlets through the chamber of gas-discharge camera.
Another TE laser with a high repetition rate of pulses is known from a Japan patent application JP2004186310. In this laser, the corona-discharge pre-ionizers are disposed on the four sides of the discharge gap, formed by continuous electrodes. However, the pre-ionizers are disposed in the gas flow zone, which increases the gas flow resistance. The gas, moving with a high velocity, forms local turbulence, which extend into the discharge gap. It does not permit effective operation at a high repetition rate of pulses. The arrangement of the pre-ionizers immediately in the flow zone near the main electrodes can lead to parasite discharges between the main electrodes through the pre-ionizers. Moreover, since the pre-ionizers are situated near the main discharge gap formed by the main discharge electrodes, electric field in the main discharge gap is distorted by the presence of the pre-ionizers, which negatively affects the quality of discharge, and decreases the uniformity of the laser light in its cross-section.